The Michael-Aldol Condensation Approach to the Construction of Key Intermediates in the Synthesis of Nimbolide and Nagilactone A

References

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• Both lactones 8 and 4 were separately hydrogenated according to the following procedure, described for the minor enone: 5% palladium on activated charcoal (2.7 mg, 0.135 mg Pd, 1.27 μmol, 0.03 equiv) was added to a solution of the enone-lactone 4 (11.6 mg, 0.042 mmol) in dry MeOH (3.9 mL). The black suspension was shaken under an H2 atmosphere (p=2 atm) during 90 min. The reaction mixture was filtered through a short pad of celite, and the filtrate was concentrated to yield the hydrogenated product 10 (11.7 mg, ∼100%)
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• Dihydroderivative of the major lactone (9): 1H NMR δ 4.19 (t: J= 2.8 Hz, 1H, H-1), 3.69 (s, 3H, CO2CH3), 3.14 (d: J=1.6 Hz, 1H, H-9), 2.70–2.00 (m, 8H), 1.87 (dd: J= 2.0, 12.2 Hz, 1H, H-5), 1.32 (s, 3H, 4-Me) and 1.04 (s, 3H, 10-Me). 13C NMR δ 202.00 (q, C-8), 175.99 (q, CO2CH3), 171.05 (q, C-11), 83.26 (CH, C-1), 66.53 (CH, C-9), 51.56 (CH3, OMe), 46.45 (q, C-10), 45.40 (CH, C-5), 42.59 (q, C-4), 41.51 (CH2, C-7), 31.75 (CH2, C-3), 27.06 (CH3, 4-Me), 21.67 (CH2, C-6), 21.46 (CH2, C-2) and 15.54 (CH3, 10-Me).
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